Actor Gary Oldman has joked that his casting as legendary former prime minister Winston Churchill was a “ridiculous” choice.

The Harry Potter star said the “physicality” of the heavy politician was the most challenging part of the role and required four hours in make-up every day.

He plays the wartime leader in Joe Wright’s big screen release Darkest Hour, looking back over Churchill’s time in office.

Oldman told BBC Radio 4 Front Row’s Kirsty Lang: “(When I got the role) I thought it was a bit ridiculous. It was never on my bucket list, it would never have occurred to me.

Darkest Hour Premiere – London

“I am coming up to a milestone at nearly 60, so there was no way that I was going to gain 70 pounds to play him. It was the physical that was the hurdle, not necessarily whether I could psychologically play the character.”

But while the detailed transformation sometimes demanded a 1.45am start, he confessed: “It’s oddly liberating. I liken it to wearing a Halloween costume: if you have ever worn a mask, you lose your inhibitions”

With an acting career spanning four decades and roles such as Sid Vicious in Sid And Nancy, George Smiley in Tinker Tailor Soldier Spy and Potter’s Sirius Black under his belt, he has yet to claim the industry’s most prestigious acting awards.

After recently receiving his first Golden Globe nomination for Darkest Hour, he described the response to his portrayal from Churchill’s descendants as the highest accolade.

“When I was at drama school, one particular teacher used to tell me I would never amount to very much… one told me I was an idiot.

National Archives papers

“Playing this role particularly has been a real honour and a privilege. Above and beyond what accolades may or may not come my way, the Churchill family have responded to the film and particularly to the representation of him very well.

“The other week we were at Long Beach where they have a Churchill exhibition, and this voice behind me went, ‘Hello great grand-papa’. It was (Churchill’s great-grandson) Randolph. That’s my Oscar right there, you know.”

On the long-awaited nomination, which comes 20 years after he received two Bafta awards for direction of his semi-autobiographical film Nil By Mouth, he joked: “It’s the first, they’ve ignored me for 30 years, and I must be the only actor who has had one without a publicist. I am so proud of that.”

Adding that he did not always feel “comfortable” with the public element that comes with celebrity status, he continued: “People like to know how things are done and there’s always a story behind what you do. I personally don’t like to know how the rabbit is pulled out of the hat, I don’t want to go behind the curtain.

“Why can’t the work just speak for itself? Why do we have to know, as my old granny used to say, “the ins and outs of the cat’s a***hole”?”